The present invention relates to the field of electronic devices, such as integrated electronic circuits with very large scale integration (VLSI). More particularly, the invention relates to a method of low dielectric constant film deposition on a semiconductor through chemical vapor deposition (CVD) techniques for use in making such devices.
Low dielectric constant films are very important materials for insulation technology used in manufacturing VLSI electronic circuits. Currently, silicon oxide is the dielectric most used in the microelectronics industry. Yet, the trend in this industry is that the devices used in HC-MOS technology are continuously getting smaller. This reduces the average distances between the various devices and, in particular, between the single active elements of the devices.
Accordingly, there is an increasing need for low dielectric constant films which reduce the thickness of the insulation dielectric. Further, it is also desirable to reduce the effects of stray capacitance which results among the various electrically active structures due to the interposed dielectric. Hence, materials that may function as insulation dielectrics and which also have increasingly better gap-fill and step-coverage capacities are sought after.
Numerous references may be consulted for descriptions of current deposition methods. Some examples include: T. Shirafuji et al., xe2x80x9cPlasma Copolymerization of Tetrafluoroethylene/Hexamethyldisiloxane, and In Situ Fourier Transform Infrared Spectroscopy of Its Gas Phase,xe2x80x9d Jpn. J. Appl. Phys., Vol. 38, No. 7B, 1999, pp. 4520-4526; S. M. Yun et al., xe2x80x9cLow-Dielectric-Constant-Film Deposition with Various Gases in a Helicon Plasma Reactor,xe2x80x9d J. Appl. Phys., Vol. 38, No. 7B, 1999, pp. 4531-4534; Y. C. Quan et al., xe2x80x9cPolymer-like Organic Thin Film deposited by Plasma Enhanced Chemical Vapor Deposition, Using the Para-xylene Precursor as Low Dielectric Constant Interlayer Dielectrics for Multilevel Metallization,xe2x80x9d J. Appl. Phys., Vol. 38, No. 3A, 1999, pp. 1356-1358; L. M. Han et al., xe2x80x9cPulsed Plasma Polymerization of Pentafluorostyrene: Synthesis of Low Dielectric Constant Films,xe2x80x9d J. Of Appl. Phys., Vol. 84, No. 1, 1998, pp. 439-444; S. M. Yun et al., xe2x80x9cSiOF Film Deposition Using FS(OC2H5)3,xe2x80x9d J. Of Electrochem. Soc., Vol. 145, No. 7, 1998, pp. 2576-2580; V. Pankov et al., xe2x80x9cThe Effect of Hydrogen Addition on the Fluorine Doping Level of SiOF Films Prepared by Remote Plasma Enhanced Chemical Vapor Deposition Using SiF4-based Plasmas,xe2x80x9d Jpn. J. Appl. Phys., Vol. 37, No. 11, 1998, pp. 6135-6141; and Y. Uchida et al., xe2x80x9cA Fluorinated Organic-Silica Film with Extremely Low Dielectric Constant,xe2x80x9d Jpn. J. Appl. Phys., Vol. 38, No. 4B, 1999, pp. 2368-2372).
The prior art deposition methods described in the above references generally relate to the deposition of low dielectric constant films through CVD methods, such as subatmospheric chemical vapor deposition (SACVD), plasma enhanced chemical vapor deposition (PECVD), low pressure chemical vapor deposition (LPCVD), atmospheric,pressure chemical vapor deposition (APCVD), and high density plasma chemical vapor deposition (HDP-CVD). Chemical compounds called precursors are used for starting the film deposition process, which must include chemical elements that will form the chemical structure of the final film.
One typical low dielectric constant film includes fluorocarbons deposited by plasma. Another prior art film is fluorine enhanced silicon oxides (e.g., SiOF) made from mixtures of hexamethyldisiloxane (HMDSO), TFE (tetrafluoroethylene), para-xylene (P-XILENE) and pentafluorostyrene deposited by plasma-chemical methods or by fluoro-triethylsesquioxane (FTES) through CVD or fluoro silicon glass (FSG) methods deposited through HDP-CVD by a mixture of tetrafluofluorosilane and silane. Still other prior art films include the xe2x80x9cdiamond-likexe2x80x9d film provided either by high-temperature processes or with plasma techniques from hydrocarbon mixtures and sesquioxide (HSQ) and methylsesquioxane (MSQ) deposited through a xe2x80x9cspin-coatingxe2x80x9d process.
The above-described methods exhibit certain significant disadvantages. In fact, by using plasma-chemical techniques, it is not possible to control the stoichiometry of the produced film, which among other things exhibits limited xe2x80x9cgap fillxe2x80x9d and xe2x80x9cstep coverage.xe2x80x9d On the contrary, one drawback of SiOF films is the fluorine dissipation during the heating step. With respect to fluorocarbons, one important drawback is the low thermal stability at which these films may decompose after heating. That is, fluorine ions are freed which would irreversibly impair the operation of the device.
Another problem is the throughput of the films that may currently be implemented in plasma-chemical industrial processes. One attempt to address this problem is found in U.S. Pat. No. 4,938,995 to Giordano et al., and assigned to The Standard Oil Company. Films deposited in reasonable process times through xe2x80x9cspin-coatingxe2x80x9d are described in U.S. Pat. No. 5,889,104 to Rosenmayer and assigned to W. L. Gore and Associates, Inc.
Moreover, the above films may have a low dielectric constant and thermal stability above 400xc2x0 C. Nevertheless, the films deposited through spin-coating can deteriorate as a result of the treatments during the plasma phase to which the device is subjected and during the machining steps subsequent to the deposition. This is because of the properties of such films which behave as insulators and interact with oxygen (O2). Further, the high porosity of these films results in a low dielectric constant and may make them unreliable for use in a process flow for manufacturing microelectronics devices. Moreover, a significant disadvantage of poly-organic films is that they have a low resistance to thermal treatments.
Thus, in the microelectronics industry there is a need for deposition precursor compounds that provide low dielectric constant films which may readily be used for manufacturing VLSI electronic circuits.
It is an object of the invention to provide a method of low dielectric constant film deposition by using conventional CVD techniques used in the coating processes of thin films with a more advantageous class of precursor compounds (from the thermal stability standpoint), with improved film evenness and process conditions.
The present invention is directed to using a class of monomeric compounds, called organosilanes, as deposition precursors in conventional CVD techniques which are suitable for the industrialization of thin film coating processes. The method of the invention essentially includes using a class of silicon compounds bound to oxygen and to an organic portion as deposition precursors, namely organosilanes.
More specifically, a low dielectric constant film is deposited on a surface of a semiconductor substrate through CVD techniques using a class of precursor monomeric compounds including oxygenated organosilanes. The precursor monomers may include at least one silicon-oxygen-organic unit bond. The organic unit preferably is a non-substituted benzene ring or has at least one substituent selected from the group including a C1-4 alkyl, halogen, CF3 or other aromatic compounds. Advantageously, according to the invention, the monomeric compounds may have the following formula: 
where R and R1 are each equal to H, Hal, a C1-4 alkyl, CF3, a C1-4 alkoxide, NO2, or an aromatic ring (optionally substituted ), R2 and R3 each are a C1-4 alkyl, and X is a halogen (e.g., Br or Cl).